Grey-scale conversion X-ray mapping by EDS of multielement and multiphase layered microstructures

Area of Science:

• Materials Science
• Analytical Chemistry
• Surface Engineering

Background:

• Layered engineering surfaces, such as MCrAlY coatings on turbine blades, are crucial in high-performance applications.
• Characterizing compositional changes, especially interdiffusion, in these complex microstructures is challenging.
• Traditional point-by-point scans can be time-consuming and may lack sufficient statistical accuracy.

Purpose of the Study:

• To develop a novel procedure for grey-scale conversion of energy dispersive spectroscopy (EDS) X-ray maps.
• To enable accurate plotting of line composition profiles across modified layered engineering surfaces.
• To provide a rapid and statistically improved alternative to existing methods for compositional analysis.

Main Methods:

• Collection of grey-scale elemental maps using EDS.
• Calculation of mean grey-scale levels along defined strips parallel to the layered microstructure.
• Conversion of grey-scale line profiles into quantitative composition line profiles.

Main Results:

• The developed procedure was successfully applied to a plasma-sprayed MCrAlY coating on a nickel-superalloy turbine blade.
• Compositional profiles were accurately obtained for layered microstructures after long-term isothermal heat treatments with significant interdiffusion.
• The method demonstrated significantly improved counting statistics compared to traditional point-by-point scans for equivalent scanning electron microscope time.

Conclusions:

• The grey-scale conversion method is effective for analyzing multielement and multiphase layered microstructures.
• This procedure offers a rapid and accurate alternative to EDS spectrum imaging for compositional profiling.
• The obtained composition profiles facilitate comparison with multicomponent thermodynamic modeling of interdiffusion processes.